Oil or other hydraulic fluid used to operate hydraulic systems, such as a truck bed hoist cylinder of a machine such as an off-road truck may also be used to cool the brakes of the machine. The oil may be circulated to one or more brake coolers by the main hydraulic pump except when the main hoist cylinder is activated to raise the truck payload bed. Upon demand, the oil flowing through the brake cooler may be redirected to the main hoist cylinder to raise the truck payload bed. This change in flow from the brake cooler to the main hoist cylinder and other changes in the flow path of oil or operation of the machine may cause a spike in fluid pressure, also known as an fluid hammer, in the brake cooler hydraulic circuit. This spike in fluid pressure has been linked to premature failure in seals in the brake cooler or related components.
WO 2013/112109 A1 (the “109 publication) discloses an unloading valve that uses two pilot orifices to prevent spool oscillations due to sudden pressure fluctuations. The 109 publication fails to teach an unloading valve that relieves pressure from a brake cooling line responsive to pressure changes in the cylinder end of a hoist hydraulic line.